The present invention relates to circular saw blades and to methods for making and repairing such blades. More specifically, the invention relates to circular saw blades used in so called cold sawing machines for steel and non-ferrous metals. These sawing blades conventionally comprise a center disk made of cheaper material and teeth segments, hereafter simply referred to as segments. These segments are made of high alloy and hardened material removably secured to the center disk in such a manner that individual segments, which have been damaged or all segments which have been worn out may be replaced without limiting in any way the reuse of the center disk.
One quite well known and widely used releasable interconnection between the disk and the segments is produced by milling about 1/3 off along the circumference on both sides of the center disks so that a circumferentially extending center ridge is produced having a width corresponding to about 1/3 of the thickness of the disk. The radial width of the center ridge may, for example, be about 15 mm. A groove is machined into the inner edge of the segments to receive the center ridge of the disk. The reverse construction of the interconnection between the segments and the disk is also known. In other words, the center disk is provided with a circumferentially extending center groove instead of a ridge and the segments are provided with such a ridge fitting into the groove of the disk. In any event, the overlapping portions of the segments and disk are provided with holes, and rivets extend through these holes, whereby the rivet heads are countersunk on both sides of the saw blade. For example, the countersunk holes may have an opening angle of about 90.degree.. Depending on the type of construction, the countersunk holes may be provided in the segments or in the disk. It is further known to precisely hold the segments in the plane of the disk by means of rivets extending through respective holes located where two adjacent segments abut each other. In other words, these holes extend partially through each of the two adjacent segments and this applies also to the countersunk holes. In order to replace individual segments or to remove all segments, it is necessary to punch-out the rivets.
The just described interconnection between disk and segments is rather expensive. Additionally, it is necessary that the holes through the disk along its circumference and the holes in the segments are rather precisely spaced in order to assure the necessary alignment and proper positioning of the segments.
In order to obviate the need for such rivet holes, especially in connection with so called discard saw blades attempts have been made to weld the segments to the disks either electrically or autogenously. However, difficulties have been encountered in connection with such welding attempts due to the fact that the segments expand especially in their longitudinal plane due to the welding heat. As a result, the end of a segment partially welded to the disk gaps away from the disk, thus making it difficult or impossible to properly complete the welding. This gapping away of the segments from the disk is in the plane of the disk. In addition, the welding heat causes tension forces at the welding location. These tension forces tend to bend the end of the segment not yet welded out of the plane of the disk toward the welding apparatus.
The just described difficulties have been reduced to some extent by welding the segments to the disk by means of an electron beam, whereby a substantially smaller heating zone is created. However, even such smaller heating zones do not entirely remove the difficulties of the bending of the segments.
It is well known that the tilting angle, that is, the angle between the bent end of the segment and the plane of the disk and the angle between the bent up end of the segment and the tangent to the circumference of the disk will depend in their size on the thickness of the two elements to be welded toghether. Such thickness in turn determines the energy necessary for the welding. As a result, the degree of bending out of the plane of the saw blade and also the degree of the bending radially outwardly will increase if the thickness of the elements to be welded together increases. To alleviate these problems it has been suggested, especially in connection with an electrical welding process to provide a circumferential centrally located groove in the disk, as well as in the segments, so that only respective circumferentially extending lands to the right and left are provided in the disk as well as in the segments. After the welding the grooves form a circumferentially hollow ring space in the finished saw blade. The purpose of these inner grooves is to reduce the material thickness at the welding location and thus to also reduce the above described bending of these segments. However, even this method leaves room for improvement.
Thus, it would be possible, especially in connection with a welding apparatus employing one electron beam on each side of the saw blade to perform the welding operation on both sides of the saw blade simultaneously, whereby the forces which cause the above bending would compensate each other. In this manner the segments would remain in the plane of the center disk. However, such an apparatus is rather expensive. Similarly, it would be possible to perform repeated welding steps simultaneously on both sides of the saw blade in order to reduce the applied welding energy. As mentioned, such machines capable of welding on both sides simultaneously either continuously or in sequential steps are rather expensive, in any event substantially more expensive than a welding apparatus capable of welding on but one side of the disk at a time. Besides, it has been found that the simultaneous application of welding beams from both sides of the saw blade results in an undesirable interfering between the two welding beams, since the beams penetrate respectively into the opposite land.